In recent years, oyster beds in the Gulf of Mexico have supplied over 90% of the annual U.S. Eastern Oyster production (NMFS 2006). Before overharvesting and disease ravaged the Chesapeake Bay’s oysters, Maryland and Virginia oyster harvesters supplied the vast majority of Eastern Oysters to the U.S. market (CBPB 2004). In 2004, oyster beds in the Chesapeake Bay only contributed 0.3% of the total harvest of Eastern Oysters in 2004 (NMFS 2006).

In August 2005, Hurricane Katrina caused extensive damage to the Gulf’s oyster beds (CRS 2005). The Louisiana Oyster Task Force, however, predicted a quick recovery. Though they have not released their findings yet, the task force forecast that harvesters would recover 50% of their annual production by the end of 2005 (CRS 2005).

In Louisiana, oyster harvesters spread oyster seed (juvenile oysters that are 5mm – 20mm in length) over submerged mud bottoms at densities that range from about 200,000 to 500,000 oysters per acre (SRAC 2002). Since Eastern Oysters naturally grow in high-density oyster reefs, we chose not to subtract for this factor.

In the Gulf States, the U.S. Army Corps of Engineers and state public health departments are involved in site and operations permitting for Eastern Oyster farming (SRAC 2001). Other state agencies regulate leasing of underwater land for Eastern Oyster farming. The lease agreements generally stipulate shellfish production quotas (TNC 2002). Land-leasing regulations are especially important for natural Eastern Oyster reefs to prevent over-harvesting (Beck et al. 2004). However enforcement can be expensive and is often poor (Beck et al. 2004). Therefore, we chose to not award points for this factor.

Raising Eastern Oysters does not require feed (Matthiessen 2001). Oysters filter-feed plankton from the water.

Raising Eastern Oysters does not require feed (Matthiessen 2001).

Raising Eastern Oysters does not require feed (Matthiessen 2001).

Raising Eastern Oysters does not require feed (Matthiessen 2001).

Treatment of effluent is not necessary because raising Eastern Oysters does not require supplemental feed (Matthiessen 2001).

Oysters reefs provide important habitat to other marine organisms, including juvenile fish (Lenihan and Peterson 2004). Also, the filter-feeding activity of oysters improves water quality by removing suspended particles, excess nutrients, and phytoplankton. Oyster filter-feeding activity can enhance light penetration in the water column, stimulating growth of aquatic vegetation on the seafloor, which in turn increases oxygen levels in bottom waters (ECSGA 2002). The removal of nutrients like nitrogen helps prevent excess build up of nutrients in the water, which can lead to harmful phytoplankton blooms (U.S. EPA 2005). At the height of the Chesapeake Bay’s Eastern Oyster population, the oysters filtered the bay’s volume every 3 to 4 days (CBP 2005).

Eastern Oyster farms do not produce effluent. However, the National Shellfish Sanitation Program (NSSP) must monitor water quality in areas of Eastern Oyster cultivation, because oysters can accumulate toxins harmful to humans from polluted water or water containing high phytoplankton concentrations (e.g., red tides). State and local agencies are responsible for issuing permits, overseeing leasing of beds, exercising control over uncertified areas, monitoring water quality and classifying areas in accordance with NSSP guidelines (Kraeuter and Castagna 2001).

Eastern Oysters are filter feeders and raising them does not create effluent (Matthiessen 2001). However, in high concentrations, psuedofeces and feces produced by Eastern Oysters can have harmful environmental effects by creating areas of no or low oxygen levels. Bacteria quickly consume psuedofeces and feces, and in doing so, they take up oxygen and respire carbon dioxide. High levels of bacterial respiration causes anoxic (no oxygen) conditions, which can reduce the diversity of seafloor organisms in the affected area (DFO 2006). Generally, however, this problem is associated with growing oysters in suspended rafts not with cultivated oyster reefs. Since seeded oyster-reef operations account for the majority of U.S. Eastern Oyster production (NMFS 2006), we chose to award points here.

Eastern Oysters are native in the Western Atlantic Ocean from Labrador, Canada to Mexico, including the Gulf of Mexico. Historically, Chesapeake Bay harvesters supplied the majority of the U.S. Eastern Oysters, but production is now heaviest in the Gulf of Mexico. "Escape" from Eastern Oyster farming operations via broadcast spawning (release of eggs and sperm into the water) likely helps repopulate natural oyster beds that have been impacted by overfishing, hurricanes, and/or disease (Matthiessen 2001).

Though some Eastern Oyster production occurs on the West Coast of the U.S., West Coast operations contribute very little to the U.S. market compared to the Gulf of Mexico oyster beds. Therefore, we chose to award 2.00 points for this factor.

Diseases such as Dermo (Perkinsus marinus) and MSX (Haplosporidium nelsoni) have greatly impacted oyster populations on the U.S. East Coast, particularly in the Chesapeake Bay. In the Chesapeake Bay the diseases continue to prevent the recovery of the depleted oyster population (Paynter 2005). The diseases spread between farmed and wild Eastern Oysters, but temperature and salinity play a more important role determining the spread of the diseases than farming operations (Brown et al. 2005a). Therefore, we chose not to deduct points here.

The majority of Eastern Oysters in the U.S. market are from the Gulf of Mexico, which is within the species’ native range (Matthiessen 2001).

It is unlikely that oysters that have “escaped” would compromise the genetic integrity of wild populations. The major American producers along the Gulf Coast seed their beds with spat (larval oysters) from wild populations (Coleman 2003).

The transfer of Eastern Oysters from high to low salinity water can help reduce the incidence and prevalence of MSX (H. nelsoni) and DERMO (P. marinus) infections (Paynter 2005).

Programs such as Dermowatch, an Internet-based monitoring and modeling program, aid growers and resource managers in dealing with Dermo outbreaks. The program forecasts the intensity of infections based on environmental parameters. Dermo is most virulent in high-salinity waters and can cause high levels of Eastern Oyster mortalities. Growers use Dermowatch’s forecasts to determine when they should move their oysters to areas of lower salinity, which helps them prevent high mortality. Growers also use the forecasts to predict when they should harvest market-sized oysters before they die from the disease (Gulf Oyster Watch 2005).

MSX does not infect Eastern Oysters in the Gulf of Mexico, only Eastern Oysters along the East Coast. Chesapeake Bay harvesters deal with the disease by moving oysters to lower-salinity water and using selectively bred disease-resistant Eastern Oysters (Bower 2003). Oyster managers and harvesters also use mathematical models to simulate the possible spread and incidence of MSX.

The National Shellfish Sanitation Program (NSSP) oversees the transfer of live shellfish (spat and full-grown individuals) between states to help prevent disease problems (Kraeuter and Castagna 2001).

Eastern Oysters live in intertidal and subtidal zones of bays, inlets, and sounds and behind barrier islands (Matthiessen 2001). Growers often cultivate oyster beds in waters that are uncovered at low tide, so that they are easily accessible for harvesting (SRAC 2001).

Eastern Oyster harvesters from the Gulf States to the Chesapeake Bay States mainly use dredges and tongs to harvest oysters. Dredging is most common in the Gulf States operations, and, in Florida, tonging methods dominate (NMFS 2006).

Dredging destroys bottom habitat, decreases biodiversity in the area, and captures and kills significant numbers of non-targeted animals (Morgan and Chuenpagdee 2003). There are two ways to dredge for oysters: power dredging and sail dredging. The difference refers to how the dredge is being pulled across the seafloor: power dredging is by motorboat and sail dredging, by sailboat. In the Gulf of Mexico, harvesters use power dredging exclusively. In the Chesapeake Bay, however, where Eastern Oyster beds remain severely depleted, there is considerable debate over the use of "power" dredging in oyster beds in Chesapeake Bay. Power dredging enables harvesters to dredge more oyster beds, which can cause overharvesting and depletion; while sail-powered boats move slower and dredge less area (Morgan and Chuenpagdee 2003).

Tonging methods cause significantly less damage to the bottom habitat than dredges (Lenihan and Peterson 2004). Tongs have very long handles of either wood or metal with a rake-like end for each handle. The rake-like ends scrape the bottom to capture oysters, which harvesters then bring back onboard to release the oysters on their boat decks.

Farming Eastern Oysters enhances structural habitat diversity and improves water quality (ECSGA 2002). However, oyster dredging damages habitat (Lenihan and Peterson 2004). Since the majority of Eastern Oysters in the U.S. market are harvested with dredges (SRAC 2002; NMFS 2006), we chose to deduct here.

Harmful or lethal predator deterrents are rarely used in Gulf of Mexico oyster operations. In the Chesapeake Bay, however, chemical predator deterrents, anti-predator culturing methods, and the destruction of predators are common. Some harvesters use suction dredges to remove Oyster Drill snails and mops to remove sea stars from oyster beds (Matthiessen 2001). The mops entangle the sea stars, which harvesters then remove from their oyster beds.

Suspended raft culturing is another way of growing Eastern Oysters. This method elevates oysters in the water above their benthic predators (Matthiessen 2001; LSGC 2003) by growing them on floating wooden rafts. Therefore harvesters using suspended rafts to grow oysters do not need to use predator deterrents (Matthiessen 2001; LSGC 2003).

We did not deduct points for this factor because the majority of Eastern Oysters in the U.S. market are from seeded oyster beds in the Gulf of Mexico, where predator deterrents are rarely used (SRAC 2002; NMFS 2006).

Eastern Oyster harvesters collect seed primarily from wild oyster stocks. Using seed from hatcheries is less common due to expense. Collection of seed does not likely deplete the wild brood stock. (Matthiessen 2001).